There are many differently structured pocket-knives. For example, U.S. Pat. No. 4,347,665 to Glesser discloses a pocket-knife having a body including a pair of side portions separated by a spacer so as to define a storage cavity for a knife blade. The blade is pivotally carried by its end from a selected end of the body between a stored position and an open or operative position. A releasable lock mechanism operably carried on the body for retaining the blade in its open position. The blade is provided with a cutting edge along an underside and a cutting edge of shorter length is provided along the top side and a finger depression is formed on the blade adjacent to an enlarged portion for grasping by the thumb of the user for urging the blade from its closed position into its open or operative position.
U.S. Pat. No. 4,741,106 to Yamagishi discloses a folding pocket-knife substantially including a handle, a blade retaining lever and a blade. The blade is pivotally held in the handle wherein the engagement between a holding lever and the base of the blade, which keeps the blade out of the handle, is released by depressing the press area of the lever. The press area of the lever is covered with soft and pliable material that can be moved downward together with the press area so that the disengagement between the retaining lever and the blade can be made without pain to the finger. The whole body of the handle is covered with the soft and pliable material, but the handle may be formed with hard material except the portion over the press area so that this portion is covered with the soft and pliable material.
U.S. Pat. No. 4,985,998 to Howard discloses a knife having a foldable blade includes a locking bar which holds the blade in an open position. A release lever is provided on the side of the handle for releasing the locking bar and allowing the blade to be moved to a closed position. The release lever has a laterally exposed portion which is flush with the outer surface of a bolster of the knife and a projection which extends into the recess which receives the blade when the knife is closed. The projection engages the bottom surface of the locking bar and urges it upward when the laterally exposed portion is depressed.
The above-mentioned conventional pocket-knives have different control mechanisms to extend or fold their blades. However, all these conventional pocket-knives do not have any design to allow the blade thereof to be extended or folded in a smooth but stepped manner. In the event the blade is too loosely held in the handle, a user might be accidently injured when the blade is pushed to extend with a too strong force. On the other hand, in the event the blade is too tightly held in the handle, the user will have to exert a strong force to extend the blade even with two hands. When the blade is not extended or folded in a stepped manner, the pocket-knife tends to more easily injure the user's hand. It is therefore desirable to eliminate this drawback existed in the conventional pocket-knives.